The origin of this word comes from accounts of Mr. Henry Flanagan's pulling of what was known as "The Nine day no Shit". Flanagan accomplished this feat in the summer of 1910 after experiencing sub-stadard bathrooms, and a prolonged canoe trip excusion on open water in the South Puget Sound. It is disputed by many leading historians whether this event actually occured. Yet many witness accounts give substantial proof that this really happened.
Here is Dr. Sean Simonsen's Account
"August 5th 1910, Day 7 on the expedition, it is very hot and sunny here in the south puget sound. The sailors are getting wary and are bitchin' about how they have been paddling for so long and its not fair that I haven't paddled once over this excursion. Henry has told me that he hasn't taken a shit over these 7 days... HOLY FUCK! HE HASNT TAKEN A SHIT IN SEVEN DAYS!!! WHAT THE HELL!!!"
Although the this occurance is not yet validated, the phrase still survives.
and... trust me, It actually happened.
Guy 2: Yeah I know man, I think I'm gunna have To Pull a Flanagan.
Guy 1: But this camp is for 2 weeks!!! Man, your nasty!